High-frequency transformer



Feb. 19, 1952 E HIGH-FREQUENCY TRANSFORMER Filed July 17, 1947 One Layer Coil One Layer Call WITNESSES:

INVENTOR Reuben Le BY- M5 ATTORNEY Patented Feb. 19, 1952 UNITED STATES PATENT OFFICE HIGH-FREQUENCY TRANSFORMER Reuben Lee,Linthicum Heights, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 17, 1947', Serial No. 761,500

2 Claims. 1

This invention relates to electrical transformers and particularly to high frequency transformers.

In transformers operating at high frequency, such as from 50 to 500 kilocycles, the upper limiting operating frequency that is possible in a transformer is determined by the relation between the leakage inductance and distributed capacity of the transformer windings. These quantities can be reduced by careful design, but there is usually a physical limit to this reduction and therefore to the highest frequency at which a transformer using a given core material can be operated. The windings are usually single layer windings, that is, all turns of a given section are in one layer about the winding leg of the core, in order to keep the distributed capacitance of the winding at a minimum. Where the winding is sectionalized to reduce the leakage inductance, each section is wound in a single layer and the appropriate insulation is provided between the sections to prevent the capacitance of the winding from increasing unduly. The resulting spacing required to provide space for the necessary insulation may cancel the benefit obtained by reducing the leakage inductance.

It is an object of the invention to provide a transformer of the above-indicated character having a higher upper operating frequency than is possible with the conventional transformer construction formerly used.

Other objects and advantages of the invention will be apparent from the following description of the invention, reference being had to the accompanying drawing, in which:

Figure l is a diagrammatic view of a circuit in which the transformer of the invention may be used;

Fig. 2 is a sectional view of a transformer constructed in accordance with prior art practice; and

Fign3 is a sectional View of a transformer constructed in accordance with the invention.

Referring to the drawing, Fig. 1 is a diagrammatic illustration of a conventional circuit in which a pair of vacuum tubes I and 2 are connected to supply current to the primary winding of a transformer 3 which supplies current from its secondary winding to a balanced load illus conductor 9 and to ground at II] to establish a zero bias for the tube elements. The plates 8 of the tubes are connected to the outer or end terminals II and I3, respectively, of the primary winding of the output transformer 3, the midpoint l2 of this winding being connected to a plate voltage supply conductor B+. This midpoint l2 may be considered as grounded for high frequency through the filter capacitor of the conventional plate voltage supply. The outer or end terminals I4 and I6 of the secondary windings of the transformer are connected by conductors I8 and I9, respectively, to the outer ends of the resistors 4 and 5. The midpoint I5 of the secondary winding is connected through conductor 21 to the midpoint 22 of the resistors 4 and 5, and to ground at 23.

Fig. 2 is a sectional view of a conventional transformer used in the circuit of Fig. 1 and includes a core 24 of magnetic material having a winding leg 25 about which are positioned coils 26, 27 and 28. The coil 21 is a secondary winding sandwiched between the two coils 26 and 28, which together form the primary winding. Layers of insulating material 29, 3!] and 3| are provided within each of the three coils 2B, 21 and 28, respectively. The several coil terminals II, I2,, I3, I4, I5 and I6, shown in Fig. 2, correspond to the same numbered terminals in Fig. 1. A conductor 32 is shown at the left in Fig. 2, connecting the ends of the coils 26 and 28 together to form the midpoint I2 of the primary winding. The midpoint 33 of the secondary winding is connected to the terminal conductor I5.

Fig. 3 is a sectional view of a transformer constructed in accordance with the invention, the

terminal conductors from the several coils being numbered to correspond to the terminals shown in Fig. 1.. In the transformer structure shown in Fig. 3, a coil of magnetic material 4| is provided having a winding leg 42 about which the several primary and secondary coils are positioned. All of the transformer coils are in alignment at one end along a plane indicated by the numeral 43 which is the starting point of the winding of each of the several coils. In the structure shown in Fig. 3., there are two primary coils indicated at PI and P2, and two secondary coils indicated at SI and S2. The primary coil PI is connected between the terminals I I and I2. and the primary coil P2 is connected between the terminals I2 and I3 so that the entire primary winding is connected between the terminals II and I3, and the midpoint of this winding is the terminal I2, corresponding to the diagrammatic showing in Fig. 1. Likewise, the secondary coil SI is connee-ted between the terminals I4 and I5, and the 3 secondary coil S2 is connected between the terminals I5 and I6 so that the entire secondary winding is connected between the outer terminals I4 and I6, and the midpoint of the secondary winding is the terminal I5 between these two secondary coils.

The first turn in each of the several primary and secondary coils SI, PI, P2 and S2 starts in. the same plane 43, and the succeeding turns extend along the length of the winding leg 42 turn by turn toward the right, as shown in Fig. 3, for a distance depending upon the number of turns in the several coils. In the illustrated embodiment of the invention shown in Fig. 3, the two secondary coils SI and S2 are shown as occupying about half the space of the primary coils PI and P2. That is, the space at the right of both of the secondary coils SI and S2 is not used at all. The coils SI and S2 have about half the number of turns of the coils PI and P2. The point of connection I5 corresponding to the first turn of the secondary coils SI and S2 is on the same vertical line as the point of connection I2 of the primary coils PI and P2, which points of connection are at or near ground potential at high frequency, and, consequently, at substantially the same potential. With this arrangement of the several coils having equal volts per turn and the same number of turns per inch in the horizontal direction along the winding leg, the voltage between adjacent conductors in the associated pairs of coils PI and SI, and P2 and S2 is small. As viewed in Fig. 3, there is substantially no high frequency voltage between adjacent points in the winding turns of the coils SI and PI or between adjacent points of the coils S2 and P2. Therefore, the insulation 46 shown between coils PI and SI, and between coils P2 and S2 may be reduced to a small thicknessincreasing the mag netic coupling between the associated coils PI and SI forming a pair, and the associated coils P2 and S2 forming another pair of coils in the completed assembly. A tube of insulated material 45 is provided about which the several coils are positioned and which may be of a normal or conventional thickness necessary to insulate the innermost coil SI from the core. As above stated, the insulating layers 46 between the associated pairs of primary and secondary coils may be very thin because of the arrangement of the turns in the associated coils substantially eliminating alternating current voltages between adjacent turns in the two windings. On the other hand, a relatively thick insulating tube 41 is provided between the first pair PI and SI, and the second pair P2 and S2 of the windings to keep the effective capacitance between the coils on the opposite sides of this insulating tube at a low figure. Insulating material 48 is shown in the space to the right of the secondary coils SI and S2 not occupied by winding terminal.

It will be noted from the spacing of the several coils, as above described, that the effective capacitance between primary coils PI and P2 is low as is also the effective capacitance between the secondary coils SI and S2, because the spacing between these coils is large While the capacitance between the coils SI and PI, which are positioned closer with respect to each other, is very high, and also the capacitance between the coils S2 and P2 is very high. However, since the voltage across these high capacitances is virtually zero, the effective capacitance is also virtually zero. It Will also be noted that there is a close inductive coupling between the primary and secondary coils PI and SI, and likewise between the primary and secondary coils P2 and S2, because of the omission of most of the insulation 46 previously required in other types of construction, and the positioning of these coils more closely together than would otherwise be possible. There is also a high capacitance coupling between these closer positioned pairs of primary and secondary coils. Because of this high capacitive coupling, some of the load current can pass by capacitive coupling from coil PI to SI, and from coil P2 to S2 without traversing the Whole primary winding. Because of these characteristics, I have found that the structure shown in Fig. 3 provides approximately 60% increase in upper operating frequency over the conventional transformer formerly used and shown in Fig. 2. A transformer constructed in accordance with Fig. 2, which was incapable of giving sufficient secondary voltage at 300 kilocycles, was re-wound according to Fig. 3 and was then able to give a proper output voltage up to 500 kilocycles frequency.

In the embodiment of the invention illustrated in Fig. 3, a voltage ratio from primary to second-1 ary of about 2:1 was assumed so that the unused space at the right of the secondary coils SI and i winding leg and the primary coils being shorter leaving some unused space.

It will be apparent to those skilled in the art that modifications in the illustrated embodiment of the invention may be made within the spirit of the invention and I do not wish to be limited otherwise than in accordance with the scope of the appended claims.

I claim as my invention:

1. An electrical transformer comprising a core of magnetic material having a winding leg, primary and secondary windings about the winding leg of the core, the primary winding and the secondary winding each comprising two cylindrical coils and each coil being in the form of a helix and having a single layer of turns, the two primary coils being positioned adjacent to each other, one of the two secondary coils being positioned within the primary coils and the other secondary coil being positioned about the two primary coils, the primary and secondary coils starting at one end opposite the same portion of the winding leg of the core and extending along the winding leg of the core for distances cor-- responding to the respective number of turns, the primary and secondary coils having equal volts per turn and the same number of turns per unit length in the direction of their length, each secondary coil being closely positioned with respect to its nearest primary coil to maintain a close magnetic coupling and a high capacitance between them, and the two primary coils being spaced to maintain a lower effective capacitance between them, the two primary coils being connected together at their starting ends to form a midpoint of the primary winding, and the two secondary coils being connected together at their starting ends to form a midpoint of the secondary winding.

2. In an electrical transformer comprising a core of magnetic material having a winding leg,

primary and secondary windings about the winding leg of the core, the primary winding and the secondary winding each comprising two cylindrical coils and each coil being in the form of a helix and having a single layer of turns, the two primary coils being positioned adjacent to each other, one of the two secondary coils being positioned within the primary coils and the other secondary coil being positioned about the two primary coils, the primary and secondary coils all starting at one end opposite the same portion of the winding leg of the core and extending along the winding leg-of the core for distances corresponding to their respective number of turns, the primary and secondary coils having equal volts per turn, and the same number of turns per unit length in the direction of length of the coils, each secondary coil being closely positioned with respect to its nearest primary coil to maintain a close magnetic coupling and a 29 high capacitance between them, the two primary coils being spaced a predetermined distance from one another to maintain a low efiective capacitance between them, and solid insulating material disposed between the primary coils, the two primary coils being connected together at their starting ends to form a midpoint of the primary winding, and the two secondary coils being connected together at their starting ends to form a midpoint of the secondary winding.

REUBEN LEE.

REFERENCES CITED The following references are of record in the 

